That isn't sound logic. GM has a track record of making terrible managerial decisions, so assuming they know best is ignoring history. The people making the decisions haven't worked on self-driving cars and are not the best people to judge the technology, in fact these are the very people who twice (technically thrice, but that's another story) abandoned their own self-driving R&D which ultimately went to Google and Delphi (and another which was just completely thrown away).

You're also assuming that all of the other companies wanted to sell, which isn't true.